1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) having a touch screen function using a photoconductor, and more particularly, to an LCD having a touch screen function using a photoconductor in which a photoconductive material is deposited between an insulating substrate provided in a color filter substrate of a liquid crystal panel and a light shielding layer so that a touch position can be effectively found by variation in current or voltage due to a change in characteristics of the photoconductor in response to light supplied from outside.
2. Discussion of Related Art
Generally, an LCD is a compact and thin flat panel display with low power consumption. It is used in portable computers such as notebook computers, office automation systems, and audio/video systems.
Recent dramatic development of LCD technology has led to the creation of high-resolution LCDs capable of displaying high-resolution graphics. Also, a digitizer is being used as an input device in notebook computers.
A digitizer installed in a notebook computer can perform the same function as a cathode ray tube (CRT)-type touch screen used in a desktop computer.
The digitizer installed in an LCD is called a touch screen or a tablet, and a resistive type touch screen and a capacitive type touch screen are the most common types, one of which is selected depending on the type of detecting a user-indicating position.
The resistive type touch screen operates by separating two parallel transparent electrodes using a dot spacer and detecting a voltage variation occurring when the upper and lower transparent electrodes are in contact with each other by a pressure applied from outside. The capacitive type touch screen recognizes a position by detecting capacitance coupling using an alternating voltage supplied from outside.
In addition, an IR type touch screen detects a variation in infrared radiation emitted from outside of a panel, and a surface acoustic wave (SAW) type touch screen detects a variation in acoustic waves caused by touching a display surface.
The above-mentioned conventional touch screen panel technology is attached as a module to the outside of a display. Consequently, its structure may reduce transmittance and degrade displayed images, and it may be vulnerable to external stimuli such as scratching.
To solve these problems, a new method of placing an optical sensor device such as a photodiode or a photo thin film transistor (TFT) in a pixel of a panel and recognizing a touch by light supplied from outside, or finding a fine capacitance variation inside a panel, is being applied {c.f., W. D. Boer et al., SID'03 DIGEST 1494 (2003), Joohyung Lee et al., SID'07 DIGEST 1101 (2006)}.
However, these methods of using an optical sensor and detecting a capacitance variation decrease an aperture ratio of a pixel, thereby lowering transmittance and brightness and degrading displayed images. Also, since a detected signal is very weak, many peripheral devices are needed, which increases production costs.